1. Technical Field
The present invention relates to photovoltaic devices, and more particularly to devices and methods with passivated shallow junctions to reduce Auger recombination effects.
2. Description of the Related Art
In conventional front-contact solar cells, junctions are formed by diffusion and typically are a few hundreds of nanometers but less than 1 micron deep. Although higher doping levels are desired for increasing the splitting of quasi-Fermi levels and thus improving an open circuit voltage of the solar cell, the doping levels are chosen below 1019 cm−3 (typically the mid to upper 1018 cm−3 range) to avoid excessive Auger recombination in the highly doped region.
In conventional interdigitated back-contact (IBC) solar cells, doped regions are formed by diffusion with doping levels also below 1019 cm−3 to avoid excessive Auger recombination. In addition, at doping levels below 1019 cm−3 considerable portions of minority carriers can reach a substrate surface, and therefore be recombined at localized contact regions where metal electrodes are in direct contact with the doped regions.
Since all IBC junctions are formed with doping levels below 1019 cm−3, open circuit voltage (Voc) is limited by splitting of quasi Fermi levels (determined by doping concentration). In addition, doping levels below 1019 cm−3 do not completely shield the carriers from the substrate surface, therefore limiting the Voc due to recombination at localized metal contact areas. It is very difficult to form a high doping concentration especially in thin layers by conventional diffusion.